There are several applications that require an identification of an unknown set of video frames. For example, in the fields of advertisement broadcast verification and television audience metering, it is desirable to identify a program tuned by a tuner. While monitoring broadcast advertisements and/or program content, it would be useful to have unique identification information or codes embedded in the set of video frames. An example system that embeds codes in non-viewable portions of video is the Nielsen Media Research Automatic Monitoring Of Line-up System, (AMOL), which is disclosed in U.S. Pat. No. 4,025,851.
Many methods developed for analog television broadcasting may not be suitable for digital television (DTV). For example, in the AMOL system, codes are inserted into a vertical blanking interval of an analog National Television Standards Committee (NTSC) signal. In digital television, video information is transmitted as digital data streams, which do not provide a vertical blanking interval or its equivalent. Rules have been proposed by the Federal Communications Commission (FCC) for broadcasters to carry information that was previously carried by the analog NTSC signal in a digital Advanced Television Standards Committee (ATSC) bit stream. Close captioning is one type of data that will be inserted into the digital ATSC bit stream. However, due to steps a typical DTV bit stream undergoes during processing (e.g., compression), some of the data may be lost. One possible solution to the data loss problem is to embed identifiers in the form of images or watermarks in viewable video. However, to maintain picture quality, watermarks must be imperceptible to a human eye.
Considerable development effort has been directed to improving image watermarking techniques, especially for applications where the objective is to track ownership of video content. In these instances, the primary requirements for the embedded image or watermark are its robustness and its security features. The latter includes means for prevention of watermark modification or erasure by unauthorized users of content. Cox et al. describe these concepts in their recent publication “Digital Watermarking” Morgan Kaufman Publishers, San Diego, Calif. 2002.